As a conventional reference electrode conceived is a reference electrode that comprises, as shown in the patent document 1, a vessel where a liquid junction and a venthole are formed, an internal liquid contained in the vessel, an internal electrode immersed into the internal liquid, and a pressure adjust layer that locates between the internal liquid and the venthole and that transforms in accordance with a pressure.
Under a condition of being used at a high temperature, the reference electrode prevents a pressurized state due to thermal expansion of the air in the vessel or water vapor vaporized from the internal liquid so as to prevent the internal liquid from leaking out from the liquid junction. In addition, under a condition of being used at a low temperature, the reference electrode prevents a negative-pressurized state due to thermal shrinkage of the air in the vessel and liquefaction of the water vapor so as to prevent the air from entering into the vessel through the liquid junction part.
However, although it is possible for the reference electrode having the above-mentioned arrangement to solve the problem associated with the expansion and shrinkage of the air in the vessel resulting from the temperature at which the reference electrode is used, it is not possible for the reference electrode having the above-mentioned arrangement to solve the problem associated with the volume expansion of the internal liquid due to congelation of the internal liquid generating at a time when the reference electrode is kept at a low temperature. In other words, there are problems such that the internal liquid leaks from the liquid junction part and a boundary between the liquid junction part and the vessel, the liquid junction part is separated from the vessel and a crack is formed on the boundary between the liquid junction part and the vessel due to volume expansion of the internal liquid due to congelation of the internal liquid. Especially, in case that the reference electrode is kept in a standing state, the lower a position of the internal liquid is, the higher a concentration of the internal liquid becomes. As a result of this, the internal liquid gradually freezes from the upper surface. Then, the lower a position of the vessel is, the bigger the influence of the volume expansion is. As a result, since the inner pressure of the liquid junction part or its vicinity becomes high, it is likely to cause the above-mentioned problems.
Then it can be conceived that the internal liquid is prevented from freezing by adding an anti-freezing agent in the internal liquid, however, there are problems that not only an adverse effect is caused on the liquid junction potential by the anti-freezing agent but also a sample is contaminated by the anti-freezing agent that leaks into the sample together with the internal liquid.